JP5042763B2 - Elastic wave filter - Google Patents

Description

  The present invention relates to an acoustic wave filter, for example, a (SAW: Surface Acoustic Wave) filter.

  SAW devices use surface acoustic waves, and electrode fingers called IDTs (interdigital transducers) are placed on a piezoelectric substrate, and electrical-mechanical mutual conversion between electrical signals and acoustic waves is performed to generate frequencies. This has a selection (band filter) characteristic. SAW filters, which are one of SAW devices, are used as panda-pass filters for various communication devices, such as mobile phones, that have been improved in function and size. In recent years, wireless data communication has been increased in speed and capacity. Accordingly, there is an increasing demand for filter characteristics with low insertion loss (output power attenuation relative to input power), excellent frequency selectivity, and wide bandwidth, flatness, and miniaturization. In order to satisfy such a requirement, for example, a tapered IDT filter is advantageous.

For example, as shown in FIG. 13, such a filter 100 includes an input-side tapered IDT electrode 102 and an output-side tapered IDT electrode 103 that are tapered electrodes formed on a piezoelectric substrate 101. An elastic wave propagates from the input-side tapered IDT electrode 102 side toward the output-side tapered IDT electrode 103 side. A shield 104 is provided between the electrodes 102 and 103 to suppress coupling between the electrodes 102 and 103, and the shield 104 is configured as a square planar metal film (so-called solid film). ing.
Each of the electrodes 102 and 103 is composed of two parallel bus bars 105 each having a plurality of electrode fingers 106. In each of the electrodes 102 and 103, the electrode fingers 106 connected to the bus bar 105 face each other. Is formed as a SPLIT electrode by, for example, forming a pair of two and extending alternately to form a comb-teeth shape.

In each of the electrodes 102 and 103, the electrode finger 106 is formed so that the width of the electrode finger 106 is constant and the interval between the electrode fingers 106 and 106 is also constant with respect to the propagation direction of the elastic wave. ing. The arrangement pattern composed of the width of the electrode finger 106 and the interval between the electrode fingers 106 and 106 is designed such that a certain period unit λ is repeated. In this example, one cycle unit λ is constituted by the four electrode fingers 106 and the space region between the electrode fingers 106.
Therefore, in this filter 100, an elastic wave having the same length as the period unit λ propagates from the input side tapered IDT electrode 102 toward the output side tapered IDT electrode 103.
The length of the period unit λ is so as to gradually spread from one bus bar 105 toward the other bus bar 105 in the direction orthogonal to the propagation direction of the elastic wave, that is, the width of the electrode finger 106 and the electrode finger 106. , 106 are designed so that the distance between them gradually increases.

Thus, by gradually expanding the arrangement pattern of the electrode fingers 106 to form a tapered IDT, in this filter 100, a low frequency corresponding to a region where the cycle unit λ is wide from a high frequency corresponding to a region where the cycle unit λ is wide Therefore, the filter 100 has a wider bandwidth.
On the other hand, when the arrangement pattern of the electrode fingers 106 is gradually expanded, the inclination angle θ formed by the electrode fingers 106 is inclined with respect to the propagation direction of the elastic wave. In order to further widen the bandwidth of the frequency that propagates in the filter 100, the inclination angle θ is greater when the difference in the length of the period unit λ between the narrow area and the wide area of the period unit λ is large. It will be greatly inclined.

  By the way, there is a difference in the propagation state (propagation speed) of the elastic wave on the piezoelectric substrate 101 between the part where the input side tapered IDT electrode 102 and the output side tapered IDT electrode 103 are present and the part where it is not present. Is refracted when radiated from the edge of the input-side tapered IDT electrode 102 on the output-side tapered IDT electrode 103 side. Therefore, when the tilt angle θ of the electrode finger 106 is tilted in this way, the elastic wave propagating from the input-side IDT electrode 102 is from a track that is a propagation path in which a periodic unit λ corresponding to the wavelength is formed. It is greatly displaced and enters the output-side tapered IDT electrode 103.

  In FIG. 14, in such a filter 100, for example, two types of elastic waves of Tr 1 (low frequency side) and Tr 2 (high frequency side) have period units λ corresponding to respective frequencies in the input side tapered IDT electrode 102. When radiated from the formed track toward the output-side tapered IDT electrode 103 side, the energy distribution when the elastic wave transmitted from each track is received as it is without a track shift (on the right side in the figure) (Hatching) and energy distribution (hatching on the left side in the figure) when received with a track deviation. From FIG. 14, it can be seen that the energy received by the output-side tapered IDT electrode 103 is reduced by refraction in both the low frequency side and the high frequency side, that is, in all tracks. Comparing the degree of decrease in energy, the distance L between the input side tapered IDT electrode 102 and the output side tapered IDT electrode 103 is longer on the high frequency side of Tr2 than on the low frequency side of Tr1. As for dTr indicating the track deviation, dTr2 is larger than dTr1, and as a result, the attenuation amount of energy on the high frequency side is increased.

Further, since diffraction occurs with respect to the elastic wave radiated from the end portion of the input side tapered IDT electrode 102, energy propagation between the input side tapered IDT electrode 102 and the output side tapered IDT electrode 103 is based on diffraction. Although loss occurs, this diffraction loss also increases as the distance L between the input side tapered IDT electrode 102 and the output side tapered IDT electrode 103 increases.
For this reason, the energy loss due to refraction or diffraction has a large influence on the characteristics on the high frequency side with a long propagation distance L, and therefore the attenuation characteristics on the high frequency side deteriorate as shown by “B” in FIG.

Further, as shown as Tr0 (lower frequency side than Tr1) in FIG. 14, among the elastic waves radiated from the input side tapered IDT electrode 102, the region where the output side tapered IDT electrode 103 is formed by refraction. There is also an elastic wave that propagates to a region that is out of the range, and since such an elastic wave is not received by the output-side tapered IDT electrode 103, the attenuation characteristic is deteriorated even on the low frequency side.
On the other hand, in such a filter 100, in order to increase the selectivity, that is, in order to make the rise of the pass band in the frequency characteristic diagram steep, a technique of increasing the number of pairs of the normal electrode fingers 106 is employed. For this reason, the inclination angle θ of the electrode finger 106 is further greatly inclined, and the deterioration of the attenuation characteristic becomes more remarkable.

In summary, there are the following problems.
Since the tapered IDT is inclined, the attenuation characteristic is degraded from the low frequency side to the high frequency side, and the degree of degradation is particularly large on the high frequency side. When the band of the filter 100 is increased and when the logarithm of the electrode finger 106 is increased, the inclination angle θ increases, and this deterioration becomes particularly significant. Further, there is a problem that the size of the filter 100 increases as the number of electrode fingers 106 increases.
Patent Document 1 describes the above-mentioned problem, but does not suggest any technique for suppressing refraction and diffraction of elastic waves.

JP-A-2005-150918 ((0004), (0022) to (0025))

  The present invention has been made in view of such circumstances, and an object of the present invention is to suppress deterioration in attenuation characteristics due to refraction of elastic waves and the like in an elastic wave filter in which an IDT is configured in a taper shape. It is to provide technology to suppress.

The elastic wave filter of the present invention is
A pair of bus bars formed so as to be parallel to each other and a group of electrode fingers that are alternately extended from each of the pair of bus bars and formed in a comb-teeth shape. Tapered IDT electrodes formed so that the spacing region of the bus bar extends from one side to the other side of the bus bar are provided on the input side and the output side, respectively, spaced apart from each other in the propagation direction of the elastic wave. In an elastic wave filter in which a short grating electrode is provided between a type IDT electrode and an output side tapered IDT electrode,
The electrode finger array pattern in the short grating electrode is formed such that the electrode finger array pattern in at least one of the input-side tapered IDT electrode and the output-side tapered IDT electrode is continuously extended. It is characterized by that.

The electrode finger array pattern in the short grating electrode is formed such that the electrode finger array pattern of the input side tapered IDT electrode and the electrode finger array pattern of the output side tapered IDT electrode are continuously extended. In addition, it is preferable that the electrode fingers of the mutual arrangement pattern are joined at the intersection of these arrangement patterns.
The electrode finger array pattern in the short grating electrode is formed such that one of the electrode finger array patterns of the input-side tapered IDT electrode and the output-side tapered IDT electrode is continuously extended. And the other end of the input-side tapered IDT electrode and the output-side tapered IDT electrode on the short grating electrode side may be separated from each other.

When the period unit of the arrangement pattern of the electrode fingers corresponding to the wavelength of the elastic wave propagating in the track that is the propagation path of the elastic wave is λ,
A distance between center lines of adjacent electrode fingers in each of the input side tapered IDT electrode, the short grating electrode, and the output side tapered IDT electrode,
The distance between the center line of the electrode finger on the short side of the short grating electrode in the input side tapered IDT electrode and the center line of the electrode finger on the side of the input side tapered IDT electrode in the short grating electrode;
The distance between the center line of the electrode finger on the short grating electrode side in the output-side tapered IDT and the center line of the electrode finger on the output-side tapered IDT electrode side in the short grating electrode is λ / 4. It is preferable that
Either the input side tapered IDT or the output side tapered IDT may be a unidirectional electrode.
A part of the electrode finger group of the short grating electrode may be an elastic wave reflection source whose width is set to ¼ or less of λ.
The electrode fingers in the input-side tapered IDT electrode and the output-side tapered IDT electrode are connected to both of a pair of bus bars in each of them,
A part of the electrode fingers of the short grating electrode may be an elastic wave reflection source whose width is set to 5/8 or less of the λ.

  The present invention relates to an elastic wave filter in which a short grating electrode is provided between an input-side tapered IDT and an output-side tapered IDT, and an arrangement pattern of the short grating electrodes is defined as an input-side tapered IDT and the output-side tapered IDT. The arrangement pattern of at least one of the electrode fingers is continuously extended. For this reason, the portion of the short grating electrode that inherits the arrangement pattern of the electrode fingers of the input side tapered IDT electrode is acoustically the same medium as the input side tapered IDT electrode, and the output side tapered of the short grating electrode. The portion that inherits the arrangement pattern of the electrode fingers of the type IDT electrode is the same medium as the output side tapered IDT electrode, and therefore there is one boundary between the input side and the output side. As a result, the degree of refraction or the like of the elastic wave is reduced, and deterioration of the attenuation characteristic can be suppressed.

  An embodiment of the present invention will be described with reference to FIGS. The acoustic wave filter 10 of the present invention has an input side taper on the surface of the piezoelectric substrate 11 that has the same configuration as the input side tapered IDT electrode 102 and the output side tapered IDT electrode 103 of the filter 100 shown in FIG. A type IDT electrode 12 and an output-side tapered IDT electrode 13 are formed. The input-side tapered IDT electrode 12 and the output-side tapered IDT electrode 13 are provided at an interval with respect to the elastic wave propagation direction.

In the input side tapered IDT electrode 12, reference numerals 14a and 14b denote a bus bar on one side and a bus bar on the other side, respectively, which are formed in parallel to each other. The bus bar 14a on one side is connected to the input port 21, and the bus bar 14b on the other side is grounded.
Reference numeral 15 denotes an electrode finger in the input-side tapered IDT electrode 12, and an electrode finger group composed of the plurality of electrode fingers 15 is a set of two so as to be a SPLIT electrode. The bus bars 14a and the other bus bar 14b are arranged so as to be arranged in a staggered pattern so as to extend toward the other bus bar 14b and the other bus bar 14a facing each other.

As shown in FIG. 2, the electrode fingers 15 are formed so that the arrangement pattern including the width and the interval between the electrode fingers 15 and 15 is constant with respect to the propagation direction of the elastic wave. The arrangement pattern of the electrode fingers 15 is a length composed of a set of two electrode fingers 15 extending from one adjacent bus bar 14a and a set of two electrode fingers 15 extending from the other bus bar 14b. Are arranged so that the period unit of λ is repeated. In the elastic wave filter 10, an elastic wave having the same length as the length of the period unit λ propagates.
In this example, as described above, the four electrode fingers 15, more specifically, the four electrode fingers 15 and the interval region between the electrode fingers 15, 15 form the periodic unit λ, so that the adjacent electrode fingers 15, 15, the dimension between the straight lines passing through the center of the electrode finger 15 is λ / 4. In this example, since the width of the electrode finger 15 is λ / 8, the distance between the electrode fingers 15 and 15 is also λ / 8 (λ / 4−λ / 8 = λ / 8).

  In this arrangement pattern, the interval (pitch) between the electrode fingers 15 gradually increases in the direction orthogonal to the propagation direction of the elastic wave from the upper side to the lower side in the figure, and the widths of the respective arrangement patterns also from the upper side. It is formed so as to gradually widen as it goes downward. Therefore, in the direction orthogonal to the propagation direction of the elastic wave, the track that is the propagation path of the elastic wave spans a wide frequency band from Tr1 that is the region where the period unit λ is narrow to Tr2 that is the wide region. It will be formed. In FIG. 1, the width of the electrode finger 15 is drawn as a constant width for simplification of illustration.

  As shown in FIG. 1, the output-side tapered IDT electrode 13 includes a bus bar 14 c on one side and a bus bar 14 d on the other side, like the input-side tapered IDT electrode 12. The bus bar 14c on one side is connected to the output port 22, and the bus bar 14d on the other side is grounded. Similarly to the input-side tapered IDT electrode 12, the output-side tapered IDT electrode 13 has a constant periodic unit λ with respect to the propagation direction of the elastic wave and is orthogonal to the direction orthogonal to the propagation direction of the elastic wave. Is provided with electrode fingers 15 arranged so that the periodic unit λ extends from Tr1 to Tr2 from the upper side to the lower side. The arrangement pattern and dimensions of the electrode fingers 15 of the output-side tapered IDT electrode 13 are also the same as the arrangement pattern of the input-side tapered IDT electrode 12 described above.

  As shown in FIGS. 1 and 2, a short grating electrode 16 is formed between the input side tapered IDT electrode 12 and the output side tapered IDT electrode 13, and the short grating electrode 16 has a pair of One bus bar 18a in parallel and the other bus bar 18b are provided. A plurality of bus bars 18a and 18b extend in a direction substantially orthogonal to the propagation direction of the elastic wave (more specifically, oblique to the orthogonal direction), like the electrode finger 15 described above. The electrode finger 17 group is formed, and one end side and the other end side of the electrode finger 17 are connected to the bus bars 18a and 18b, respectively.

  Similar to the arrangement pattern of the electrode fingers 15, the electrode finger 17 has an arrangement pattern composed of a width and an interval in the direction of propagation of the elastic wave, which repeats at a constant cycle unit λ, and from one bus bar 18 a. The array pattern is formed so as to expand toward the other bus bar 18b. The arrangement pattern of the electrode fingers 17 will be described with reference to FIG. 2 described above in which the vicinity of the boundary between the input side tapered IDT electrode 12 and the short grating electrode 16 is enlarged. The period unit λ of the electrode fingers 17 is composed of the width and interval of the four electrode fingers 17 in the same manner as the arrangement pattern of the electrode fingers 15 described above, and on the input side tapered IDT electrode 12 side, the input side taper. The array pattern of the electrode fingers 15 of the type IDT electrode 12 is formed to be extended as it is. Accordingly, the distance between the center lines of the adjacent electrode fingers 17 and 17 is also λ / 4 as in the arrangement pattern of the electrode fingers 15. Further, the width and interval of the electrode fingers 17 are each λ / 8, as with the electrode fingers 15 described above.

  As for the region between the input side tapered IDT electrode 12 and the short grating electrode 16, the center line of the electrode finger 15 at the end of the input side tapered IDT electrode 12 on the short grating electrode 16 side and the short grating electrode 16, the distance from the center line of the electrode finger 17 on the input side tapered IDT electrode 12 side is set to λ / 4. Thereby, in the connection line 20 extending in a direction substantially orthogonal to the propagation direction of the elastic wave between the center lines, the cycle unit λ of the input side tapered IDT electrode 12 and the cycle unit λ of the short grating electrode 16 are It will be connected continuously without interruption. A region formed in the short grating electrode 16 so as to be continuous from the input side tapered IDT electrode 12 forms an input side region 16a.

As shown in FIG. 1 described above, on the output-side tapered IDT electrode 13 side, the arrangement pattern of the short grating electrodes 16 is formed so that the arrangement pattern of the output-side tapered IDT electrode 13 is extended, and the output A side region 16b is formed. Further, the distance between the center line of the electrode finger 15 on the short grating electrode 16 side in the output side tapered IDT electrode 13 and the center line of the electrode finger 17 on the output side tapered IDT electrode 13 side in the short grating electrode 16 also. , Λ / 4. As a result, the cycle unit λ of the short grating electrode 16 and the cycle unit λ of the output-side tapered IDT electrode 13 are continuously connected in the connection line 20 without interruption. The width and interval of the electrode fingers 17 in the output side region 16b are also set in the same manner as in the input side region 16a.
The output side region 16b and the input side region 16a described above are joined along a line 19 that passes through the approximate center of the short grating electrode 16 and extends in a direction orthogonal to the propagation direction of the elastic wave.
The width of the electrode finger 17 is also drawn as a constant width in FIG. 1 for simplification of illustration. In FIG. 2, the input side tapered IDT electrode 12 and the short grating electrode 16 are hatched so as to be easily distinguished.

  In such an acoustic wave filter 10, when a frequency signal is input to the input side tapered IDT electrode 12, that is, when a frequency signal is input between the input port 21 and the ground, elasticity that is an acoustic wave is generated. Surface waves (SAW) are generated. This elastic wave propagates to the output-side tapered IDT electrode 13 side in the track on which the period unit λ corresponding to the wavelength length (λ) is formed in the input-side tapered IDT electrode 12. This elastic wave is refracted every time it enters and exits the electrode finger 15, but the shape of each electrode finger 15 and the shape of the spacing region (arrangement pattern) are constant, as shown in FIG. Propagating in a straight line.

  Further, since the arrangement pattern of the electrode fingers 15 of the input side tapered IDT electrode 12 is inherited in the short grating electrode 16, the elastic wave is incident on the short grating electrode 16 from the input side tapered IDT electrode 12. In addition, the light propagates linearly in the short grating electrode 16.

In the short grating electrode 16, the boundary between the input side region 16a where the array pattern of the input side tapered IDT electrode 12 is inherited and the output side region 16b where the array pattern of the output side tapered IDT electrode 13 is inherited. Since the line 19 which is a part is a discontinuous surface, the elastic wave is slightly refracted in the line 19, but the degree is extremely small. Therefore, the elastic wave propagating from the input side tapered IDT electrode 12 through the input side region 16a propagates substantially linearly to the output side region 16b.
Thereafter, similarly, the elastic wave propagates from the output side region 16b where the array pattern of the output side tapered IDT electrode 13 is inherited to the output side tapered IDT electrode 13 in a state where refraction and diffraction are suppressed. .

  Therefore, as shown in FIG. 4, the elastic wave radiated from the input-side tapered IDT electrode 12 reaches the output-side tapered IDT electrode 13 in a state where the track deviation is suppressed over a wide frequency band. Become. In addition, the straight lines L1, L2, and L3 in the figure indicate the propagation paths (tracks) of the elastic waves that propagate at each of the three positions in the length direction of the electrode fingers 15 and 17. In this case, the wavelength becomes longer in the order of L1 <L2 <L3. The acoustic wave filter 10 actually has tracks corresponding to the wavelengths between the minimum track Tr1 and the maximum track Tr2 of the electrode fingers 15 and 17. Thereafter, an electrical signal corresponding to the elastic wave of each track is output.

  According to the above-described embodiment, the short grating electrode 16 is formed by the plurality of electrode fingers 17 instead of the metal solid film, and the input side region adjacent to the input side tapered IDT electrode 12 of the short grating electrode 16 is formed. 16a and the output-side region 16b adjacent to the output-side tapered IDT electrode 13 are continuous (extending) patterns from the input-side tapered IDT electrode 12 and the output-side tapered IDT electrode 13, respectively. . As described above, in the region between the input side tapered IDT electrode 12 and the output side tapered IDT electrode 13 and the short grating electrode 16, the cycle unit λ which is a repeating unit of the electrode fingers 15 and 17 is set. It is set to be continuous without interruption.

  From this, the acoustic wave filter 10 is apparently composed of an input-side tapered IDT electrode 12 and an output-side tapered IDT electrode 13, and the input-side tapered IDT electrode 12 and the output-side tapered IDT in each track. The boundary portion with the electrode, that is, the non-periodic structure is a periodic structure at only one position of the line 19. Therefore, the degree of refraction and diffraction of the elastic wave is small and the reflection is also small, so that the loss of elastic wave energy can be reduced in each track. As a result, as indicated by “A” in FIG. 5, the attenuation characteristic is improved, and in particular, the attenuation characteristic on the high frequency side can be improved. The shape factor (ratio of 35 dB bandwidth to 1 dB bandwidth) is 1.70 in the present invention (FIG. 5), which is a very good value, but 1.81 in the conventional method (FIG. 15). there were. Furthermore, since the attenuation characteristic is improved without increasing the number of pairs of electrode fingers 15, there is an advantage that the elastic wave filter 10 can be reduced in size. When the logarithm of the electrode fingers 15 is increased, it is possible to suppress the deterioration of the attenuation characteristics and increase the selectivity.

  Although not shown in the above example, a reflector is provided in a region outside the input-side tapered IDT electrode 12 or the output-side tapered IDT electrode 13 (a region opposite to the short grating electrode 16). It is preferable.

  In the above example, the input side region 16a and the output side region 16b are formed so that the line 19 is formed at the center of the short grating electrode 16. For example, the input side region 16a or the output side region 16b One may be enlarged so that the line 19 is inclined with respect to the propagation direction of the elastic wave (see FIG. 6).

Further, the short grating electrode 16 may be constituted by only one of the input side region 16a and the output side region 16b. FIG. 7 shows an example of such an acoustic wave filter 10. In this case, the line 19 is apparently formed between the input side tapered IDT electrode 12 and the short grating electrode 16. The Rukoto. Further, as shown in FIG. 8, the line 19 may be bent halfway, and as shown in FIG. 9, the line 19 may be bent at a plurality of places, for example, two places. In other words, each track may be designed so that there is one discontinuous surface (line 19) through which the propagating elastic wave passes.
In the elastic wave filter 10 having these configurations, the same effects as those of the above-described example (FIG. 1) can be obtained.

  Further, as shown in the above examples, the electrode fingers 15 and 17 are continuously and linearly expanded. However, as shown in FIG. As shown, it may be expanded step by step so that it becomes a pseudo taper type. 10 and 11, as in the above examples, the arrangement pattern composed of the widths and interval regions of the electrode fingers 15 and 17 is widened from the upper side to the lower side in the drawing. Although arranged, it is omitted for simplification of illustration.

  In the above example, the width of the electrode fingers 15 and 17 and the distance between the electrode fingers 15 (17) and 15 (17) are λ / 8, respectively, but may be other than λ / 8. In that case, the dimension between the straight lines passing through the centers of the adjacent electrode fingers 15 (17) (the sum of the width of the electrode fingers 15 (17) and the interval between the electrode fingers 15 (17), 15 (17)). The electrode fingers 15 and 17 may be formed so that) becomes λ / 4.

  Further, as shown in FIG. 12, a reflection source 31 that is an electrode finger having a width of, for example, λ / 4 or 3 / 8λ is provided on the input side tapered IDT electrode 12, the output side tapered IDT electrode 13, and the short grating electrode 16. A DART (Distributed Acoustic Reflection Transducer) electrode or an EWC-SPUD (Electrode Width Controlled-SPUDT) electrode may be provided between the basic electrode fingers (electrode fingers 15 and 17) having a width of λ / 8. When the electrode fingers 15 of the input side tapered IDT electrode 12 and the output side tapered IDT electrode 13 are connected to both the bus bars 14a (14c) and 14b (14d), respectively, The width of 31 may be 5 / 8λ or less.

  In this example, as in the above example, the unit of period λ is defined by the four electrode fingers 15 (17) and the interval region between the electrode fingers 15 (17), but the input side tapered IDT electrode 12 and the output In the side-tapered IDT electrode 13, one electrode finger 15 extending from one bus bar 14a, 14c and three electrode fingers 15 extending from the other bus bar 14b, 14d arranged adjacent to the electrode finger 15; A period unit λ is constituted by a set of. FIG. 12 shows an example in which a reflection source 31 is provided in the elastic wave filter 10 of FIG.

  Also in the elastic wave filter 10 having such a configuration, the loss of energy is similarly suppressed and the elastic wave propagates, and the same effect as in the above example can be obtained. In this elastic wave filter 10, by using multiple reflections actively, the loss can be further reduced and the selectivity can be enhanced. Further, by providing the reflection source 31 in this way, it is possible to reduce the loss without increasing ripple due to TTE (triple transit echo).

  In addition to such a configuration, the unidirectional electrode may be, for example, an FEUDT (Floating Electrode Type Uni-Direction Transducer) electrode or a DWSF-SPUD (Differential Width Split-Spud) electrode. Furthermore, any of these unidirectional electrodes may be used as the input side tapered IDT electrode 12 or the output side tapered IDT electrode 13 shown in FIG. Even in that case, the same effect as the acoustic wave filter 10 of FIG. 12 can be obtained.

As the input-side tapered IDT electrode 12 and the output-side tapered IDT electrode 13, two electrode fingers 15 are alternately arranged as a pair so as to be a SPLIT electrode, but one electrode so as to be a single electrode. The fingers 15 may be alternately arranged.
In the above example, a pair of the input side tapered IDT electrode 12 and the output side tapered IDT electrode 13 is formed on the piezoelectric substrate 11, but two or more pairs may be formed.
Further, the filter 10 described above may be one using an elastic wave propagating inside rather than the surface layer of the piezoelectric substrate 11 instead of a surface wave.

It is a top view which shows an example of the elastic wave filter which concerns on embodiment of this invention. It is the top view which expanded a part of above-mentioned elastic wave filter. It is the top view which showed roughly the propagation path of the above-mentioned elastic wave filter. It is the schematic which shows the mode of propagation of the elastic wave in the above-mentioned elastic wave filter. It is a characteristic view which shows the attenuation characteristic of the frequency in the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the conventional elastic wave filter. It is the schematic which shows the mode of propagation of the elastic wave in the above-mentioned conventional elastic wave filter. It is a characteristic view which shows the attenuation characteristic of the frequency in the above-mentioned conventional elastic wave filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Elastic wave filter 12 Input side taper type IDT electrode 13 Output side taper type IDT electrode 15 Electrode finger 16 Short grating electrode 16a Input side region 16b Output side region 17 Electrode finger 19 Line 20 Connection line

Claims (7)

A pair of bus bars formed so as to be parallel to each other and a group of electrode fingers that are alternately extended from each of the pair of bus bars and formed in a comb-teeth shape. Tapered IDT electrodes formed so that the spacing region of the bus bar extends from one side to the other side of the bus bar are provided on the input side and the output side, respectively, spaced apart from each other in the propagation direction of the elastic wave. In an elastic wave filter in which a short grating electrode is provided between a type IDT electrode and an output side tapered IDT electrode,
The electrode finger array pattern in the short grating electrode is formed such that the electrode finger array pattern in at least one of the input-side tapered IDT electrode and the output-side tapered IDT electrode is continuously extended. The elastic wave filter characterized by the above-mentioned.   The electrode finger array pattern in the short grating electrode is formed such that the electrode finger array pattern of the input side tapered IDT electrode and the electrode finger array pattern of the output side tapered IDT electrode are continuously extended. 2. The acoustic wave filter according to claim 1, wherein electrode fingers of each other of the array patterns are joined at an intersection of these array patterns.   The electrode finger array pattern in the short grating electrode is formed such that one of the electrode finger array patterns of the input-side tapered IDT electrode and the output-side tapered IDT electrode is continuously extended. 2. The elastic wave filter according to claim 1, wherein an extended end of the first side and the end on the short grating electrode side of the other of the input side tapered IDT electrode and the output side tapered IDT electrode are separated from each other. When the period unit of the arrangement pattern of the electrode fingers corresponding to the wavelength of the elastic wave propagating in the track that is the propagation path of the elastic wave is λ,
A distance between center lines of adjacent electrode fingers in each of the input side tapered IDT electrode, the short grating electrode, and the output side tapered IDT electrode,
The distance between the center line of the electrode finger on the short side of the short grating electrode in the input side tapered IDT electrode and the center line of the electrode finger on the side of the input side tapered IDT electrode in the short grating electrode;
The distance between the center line of the electrode finger on the short grating electrode side in the output-side tapered IDT and the center line of the electrode finger on the output-side tapered IDT electrode side in the short grating electrode is λ / 4. The elastic wave filter according to any one of claims 1 to 3, wherein   5. The acoustic wave filter according to claim 1, wherein one of the input-side tapered IDT and the output-side tapered IDT is a unidirectional electrode.   The part of the electrode finger group of the short grating electrode is an elastic wave reflection source having a width set to ¼ or less of the λ. Elastic wave filter. The electrode fingers in the input-side tapered IDT electrode and the output-side tapered IDT electrode are connected to both of a pair of bus bars in each of them,
4. A part of the electrode finger group of the short grating electrode is an elastic wave reflection source having a width set to 5/8 or less of the λ. Elastic wave filter.

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